1. Field of the Invention
The present invention relates to a package for housing an electronic component. The invention also relates to a lid material for a package lid and to a production method for the lid material.
2. Description of Related Art
Packages for housing various electronic components such as semiconductor devices (ICs) and piezoelectric vibrators generally comprise a case having an open top and a housing space for the electronic components, and a lid fuse-bonded to a peripheral upper surface of the case for hermetically sealing the housing space.
The lid comprises a core plate such as formed of an iron-nickel (Fe—Ni) alloy, nickel (Ni) layers formed on opposite surfaces of the core plate, and a brazing material layer formed on one of the Ni layers by press-bonding a brazing material foil onto the Ni layer. The formation of the Ni layers is conventionally achieved by plating the core plate with Ni.
The package is assembled by placing the lid on the top of the case with the brazing material layer of the lid facing the open top of the case, and heating the lid to melt the brazing material layer so that the lid is fuse-bonded to the peripheral upper surface of the case. Exemplary methods for the heating of the lid are to hold a heating device in contact with the lid, to heat a case-and-lid assembly in a hot oven, and to irradiate the lid with an electron beam or a laser beam.
Since the Ni layer of the lid is formed by the Ni plating, formation of pin holes in the Ni layer and contamination with an impurity such as an additive contained in a plating solution are inevitable. The pin holes present in the Ni layer are not completely crushed when press-bonding the brazing material foil onto the Ni layer, so that micro-holes remain in the Ni layer. The impurity present in the Ni layer reduces the ductility of Ni, so that micro-cracks are liable to develop in the Ni layer during the press-bonding of the brazing material foil.
The presence of the micro-holes and the micro-cracks in the Ni layer tends to result in non-uniform fuse-bonding of the lid to the case. If a non-uniform fuse-bonded portion is formed, the portion permits communication between the inside and outside of the case. Further, the micro-holes and the micro-cracks present in the Ni layer of the lid facing the opening of the case permit easy communication between the inside and outside of the case. This reduces the hermeticity of the package in which the electronic components are housed. With a recent rapid increase in precision and complexity of electronic components, packages for the electronic components are required to have a higher hermeticity.